of a share ever's deputy in the u.s. state of texas. the district attorney says deputy darren go forth was shot 15 times. >> now even though officials say that miles is cooperating with police, they still do not know what his motive was. we're also learning that miles has a history of mental illness and was once found too mentally incompetent to stand trial. here's our ed lavandera with more. >> reporter: we've learned that in october of 2012, shannon miles was arrested and criminally charged of aggravated assault with a deadly weapon, but i was found mentally incompetent to stand trial and sent to a state mental hospital for six months. this comes after prosecutors detailed in the most excruciating way some of the details of how this murder